Cons: Performs less acceptably with a totally discharged iPod, getting 4-5 hours of play time and becoming unstable in providing completely consistent power halfway through the discharge cycle. No indication of how much power is remaining; requires you to buy extra batteries.

The furor over iPod battery life has quieted down since Apple boosted the run times of various new iPods from eight or fewer hours to an industry competitive twelve or more hours per model. Outside of seriously demanding applications - say, an extended trip without access to a power outlet - the need for a super-powerful external battery has thankfully diminished, and an increasing number of companies have decided to offer lower-capacity add-ons instead of competing with BTI’s award-winning iPod Batteries (iLounge ratings: A, A-) on horsepower.

Griffin’s TuneJuice ($19.99) is the latest low-capacity battery pack to appear on the market, and it’s also the least expensive - a major asset. For the price, you get a small, glossy white rectangular box with a Dock Connector cable that connects to any iPod or iPod mini, as well as a single 9-Volt battery that pops inside the box to provide power. When connected, TuneJuice promises “up to 8 hours” of extra playtime for an iPod with some remaining battery charge, and “up to 4 hours” for a completely drained iPod. There are no status indicator lights, a power switch, or any additional frills - just the word “TuneJuice” in gray on the front, and a textured set of dots to help you pop open the battery compartment.

Griffin’s numbers proved generally accurate in our standard testing (backlight off/equalizers off/volume at 50% with earphones attached) with a first-generation iPod mini, though we found that the TuneJuice essentially requires a hint of battery power - say, 2-5% - to operate in a way that seems “right.” So long as the battery’s not discharged - indicated by a dead battery icon or a screen saying that no power remains - we saw TuneJuice run for a hint over eight and a half hours, though the 9-Volt battery did not appear to be providing consistent charge throughout the second half of its life. Once an hour starting around the third hour, the iPod’s backlight would turn on twice - once to indicate that it was running on the internal battery, and then again to indicate that it was back to running off of TuneJuice.

This contrasts with its performance with a drained iPod mini, where a four- to five-hour run time was typical. At that point, instead of flipping the backlight on twice, the iPod would reset, flipping endlessly back and forth between an Apple icon and a dead battery screen. This happened consistently at around the half-discharged point with any battery we tested, including the fresh-out-of-package standard Duracell, E2 Energizer Titanium, and generic packed-in battery. In other words, and stated a bit differently from Griffin’s explanation, if your iPod doesn’t have enough of its own juice to keep running when TuneJuice becomes unstable, you won’t be able to make anything of the 9-Volt’s second half of power.

We’ve repeatedly opined that more low-capacity rechargeable batteries such as Belkin’s TunePower (iLounge rating: B-, $99.99, 8+ hour power) and Nyko’s iBoost mini (iLounge rating: B, $79.99, 10-hour+ power) face a tough hurdle in our minds because of their higher prices, and despite their thin and attractive profiles. Under the right circumstances, TuneJuice offers similar additional power at a considerably lower price, but under the wrong ones - starting with a completely dead iPod or less than perfect 9-Volts - its utility is lower. The additional expense of batteries ($3.50 or less each) is also a factor worth considering, as is the convenience of always being able to “recharge” TuneJuice on the road just by stopping at a store.

Overall, TuneJuice is a good product that we wouldn’t hesitate to recommend for a fairly common application - getting four or eight hours of extra music run time on the go. For obvious reasons, it’s not the direct rival of the more expensive battery packs we’ve seen, but at $19.99, it’s not supposed to be, and does a pretty good job anyway. It misses our B+ rating only because of its instability at lower power levels; though it’s hard to have high expectations for the price, we’d still prefer to see the iPod just turn off instead of flipping back and forth.

Editors' Note: iLounge only reviews products in "final" form, but many companies now change their offerings - sometimes several times - after our reviews have been published.
This iLounge article provides more information on this practice, known as revving.